Evaluations of Low Cost Safety Improvements Pooled Fund Study

PPT version for Printing

Flashing Beacons at Stop Controlled Intersections Results

Dr. Raghavan Srinivasan, HSRC

Background on Strategy

Alert drivers to the presence of an intersection Reduce angle crashes Initial installation costs: $2,000 to $ 100,000 Placement Options STOP Sign mounted Overhead

Literature Review

• Previous Work
  • Cribbons and Walton 1970
    • 14 rural sites
    • About 1 year before, 1 year after
  • Pant et al. 1999
    • 6 sites without and 7 with a beacon
  • Murphy and Hummer 2007
    • 34 locations in North Carolina
    • Empirical Bayes study – accounted for change in traffic volume using a linear assumption
• Safety effectiveness has not been adequately quantified

Objective

• To examine the safety impact
• Target crash types considered included:
  • Total intersection crashes.
  • Total intersection injury and fatal crashes (including fatality (K), Injury, incapacitating (A), Injury, non–capacitating (B), and possible injury (C).
  • Total intersection angle crashes.
  • Total intersection rear–end crashes.
• Determine if safety impacts are function of:
  • Area type (rural, suburban, or urban).
  • Intersection type (Two–way versus four– way stop–controlled).
  • Types of flashing beacon installations including standard and actuated.
  • Location of the beacon including stop sign or overhead.

Study Design

• Based on methodology suggested by Hauer (1997)
• Literature review to determine the average number of crashes at stop controlled intersections
• Sample size
  • Minimum: 53 intersection–years in the before period (ability to detect 20 percent reduction in crashes at 90 percent confidence level)
  • Desirable: 260 intersection–years in the before period (ability to detect 10 percent reduction in crashes at 90 percent confidence level)

Data Collection

Data Collection – North Carolina

Total number of intersections used = 64

Data Collection – South Carolina

Total number of intersections used = 42

Aggregate Evaluation Results: North Carolina

Aggregate Evaluation Results: South Carolina

Aggregate Evaluation Results: NC and SC Combined

Disaggregate Evaluation Results: Angle Crashes

Economic Analysis

• FHWA cost per crash for unsignalized intersections (FHWA–HRT–05–051)
  • $13,238 for rear–end
  • $61,114 for right–angle
• Economic Benefit
  • Based on combined results from NC and SC
  • $ 12,040 per site–year
• Costs estimated for Standard and ‘Other’ types separately
• Standard Beacons:
  • $ 27,500 initial installation costs (high value)
  • Annual Maintenance and other costs: $ 720
  • 10 year life
  • Annualized costs = $ 4,636
  • Benefit Cost ratio is 2.6:1
• ‘Other’ Beacons:
  • Initial costs range from $ 5,000 to $ 100,000
  • Benefit achieved if initial cost is less than $ 79,000
  • 2:1 Benefit/Cost ratio if initial cost is less than $ 37,000

Conclusions

• NC: statistically significant reduction in total, angle, and injury and fatal crashes
• SC: very little change
• NC and SC combined: statistically significant reduction in angle and injury and fatal crashes
• Probably more effective in rural and suburban locations
• Very few locations with stop sign mounted beacons
• Standard beacons provide a benefit cost ratio of 2.6:1
• Net benefit of non–standard beacons depends on their cost

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